WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.

Voxer - Turn your phone into a Walkie Talkie. Don't waste time on phone calls and voicemails.

Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.

NextPlane - NextPlane offers cloud-based, scalable unified communications federation service for the enterprise.

Zulip - Chat for distributed teams. Zulip combines the immediacy of real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.

Sameroom - Chat interoperability-as-a-service